Tracepath
Perform a new query
Enter any domain name, or host ip address you would like to perform a 'Tracepath' to. (i.e. isc.org or 8.8.8.8)
Tracepath is a tool that uses ICMP pings of various sizes in order to determine the MTU values on the path between w3dt.net and the target host. Tracepath will output results as a traceroute like mode where it will attempt to determine the lowest MTU between the local host and each hop in the communication. The utility generates maybe 100 times as much traffic as a normal ping does, so you should exercise restraint when running it on networks you do not administer.
Tracepath sends a non-fragmentable icmp probe to the target IP address with a given payload size. Since the do-not-fragment bit is set, any network equipment that has an MTU setting which is smaller than the packet size will drop the packet.
Based on the presence or absence of a response, Tracepath adjusts the payload size of its next probe. Subsequent probes are sent with a packet size midway between the highest value for which a response was received and the lowest value for which a response was not received. (For the initial conditions, the low value is 0 and the high value is whatever you set with -m, defaulting to 10000 bytes).
This process is repeated, narrowing the search space by ~50% with each cycle, terminating once the highest possible probe size has been converged upon. It then adds the 28 bits of ICMP protocol overhead before reporting results.
Since each probe has to traverse the entire distance from localhost to a given hop, the reported MTU values represent the smallest MTU setting between you and the given hop, not necessarily the MTU setting between a hop and its immediate predecessor. For instance, if the MTU is narrowed on a hop midway between you and your destination, all subsequent hops will show the same small size - as your packets to more distant hops must pass through that choke point.
For example:
despite the MTU value widening past hop C, Tracepath would display the narrow, green size for both hop D and the destination host.
The w3dt Tracepath tool is based off Alexey Kuznetsov's tracepath.c
